Electrically conductive composition and method of manufacture thereof



ELEC'I'RICALLY CGNDCIVE COMPDSITION F MANUFACTURE TE-EREOF Robert W. Fritts, Eim Grove, Wis., and Sebastian Karrer,

Port Republic, Md., assignors t Baso Inc. a corporation of Wisconsin Applicaton June 1, 1955, Serial No. 512,418

9 Claims. (Cl. 75-166) alloys or compositions of the character indicated, the

resistivity of which may be controlled in magnitude as deired.

A further object of the invention is to provide electrically conductive alloys or compositions as aforementioned, in which desired resistivities therefor are reproducble.

Another object is to provide electrically c0nductive alloys or compositions of the character indicated, the thermo-electric power of which may be controlled in magnitude as desired.

A further object is to provide electrically conductive alloys or compositions as aforernentioned, having new relationships of thermoelectric power and resistvity, and which are readily reproducible within desired ranges of such relationships.

A further object of the invention concerns a method of fabrication of the aforementioned alloys or compositions to provide for the reproducible production thereof within desired ranges of thermoelectric power and resistivity.

A further object is to provide alloys or compositons as aforementioned having adequate mechanical strngth for practical applications.

A further object is to provide electrically conductive alloys or compostions of the character abovementioned which are chemically stable over a temperature range up to 400 C. when shielded rom oxdizing atmospher.

A further object is to provide electrical conductors composed of the alloys or compositions of the present invention.

Now, in order to acquaint those skilled in the art with the manner of practicng and utilizing the present invention, there is hereinafter disclosed certain preferred embodiments of the invention.

In the drawings:

Fgure 1 is a graphic illustration of the resistivity characteristics of the 'electrically cond-uctive semi-metallic alloys or compositions of the invention, within certain ranges of additions of positive promoters thereii1: and

Figure 2 is a gra'phic illustration of the thermo-electric power .characteristics of the electrically conductive semimetaliic alloys or compositions depicted in Figure 1.

The invention described and clairned herein utilizes a lead-tellurium base composition or alloy consisting essen tially of lead in the range of 59.0% t061.8% by weight,

Z811441 Patenteti ct. 2.9, 1957 balance substantially a1l tellurium, and which base com positon contains not more than 0.001% by weight of other matter.

Lead-tellurium base alloys within the aforementioned range and of the aforementioned purity are positive electrical conductors and exhibit high positive thermoelectric power, nominally higher electrical resistivity, and low therrnal conductivity wth respect to a metal. Such compositons or alloys have utility as electrical conductors. In iead-tellurium base alloys of the aforementioned range and purity, the magnitudes of the thermoelectric power and electrcal resistiviry of the aforementioned base lead-tellurium alloys can be varied only through a 1irnited range, since such characteristics are, we have found, strongly dependenbupon the equilibrium temperature from which they are cooled durng fabrication.

The aforementioned lead-tellurium alloys may be best described metallographically as a two-phase alloy. It has been observed that these ailoys, when sectioned and examinedmicroscopically, comprise a major phase com prising crystal grains varying usually from 1 to 10 millimeters in size and between such grans there exist thin relatively lighter regions of a second phase. 'Ihe grains ot theprimary phase are crystals of the intermetallic compund lead-telluride which contain approximately 6 1.88% lead by weight. The lighter second phase, clearly discernible at the grain boundaries, is tellurium containing a minor concentration of lead.

The function of the second phasein such alloys is thought to be threefold. Frst, thethermal equilibrium between the two phasles, which is established by the heat treatment aforementioned, induces positive thermoelectric power and conductivity in the primary leadtelluride phase which, because of its high concentration in the alloy, controls the electrcal properties of the two-.

phase alloy. Secondly, the thin layers actas a cementing agent for the grair1s of the primary phase, thereby irnproving the mechanical strength of the alloy when compared to that of the pure intermetallic compound.

This cementng actionof the second phase improves the strength of an alloy in tension and compression at all temperatures up to 400 C. Thirdlythe second phase affords goed electrical continuity in thepolycrystaliine alloy by rendering the intergranular component of electrical resistivity negligible- We have found that the actual concentration of second phase is not crtical so long as the composition is maintained within the aforementioned specified ranges.

Lead-tellurium alloys contaning less than 38.2% tellurium by weight do not usually exhibit reproducible physical and electrical propertes when in a polycrystalline state, and in alloys containing more than 41.0%te11urium by weight the second phase regions are of such dimension that the electrical conductivity along the grain boundaries of the alloy cannot be neglected when compared with the conductivity through the prirnary phase. Moreover, unless the specified purity is adhered to, thirdelement promotershereinafter described will not afiord reproducibility' of electrical characteristics in the resultant alloy. Accordngly, the specified composition ranges and purity are to be considered critcal.

It will be observed that since the lead-telluriurn base alloys must be slowly cooled from the annealing tem perature .to afford adequate strength, little variation-in the electrical properties can be afforded by altering the temperature of the anneal. Accordingly, for applications requiring greater variations of such values of electrical characteristics arbitrary changes in these characteristics must be derived from the adjustment of factors other than temperature and annealing history.

We have discovered that the electn'cal characteristics of lead-tellurium base alloys or compositions of the afore" We claim:

1. An alloy containing as two of its essential constituents lead and tellurium, the percent by weight of lead being 59.0% to 61.8%, balance substantially all tellurium, and the alloy containng no more than 0.001% by weight ether matter except for limited etectve amounts of a promoter from the group consisting of sodium, potassium and thallium afiordng the alloy reproducible variation of and control over the electrcal properties thereof.

2. A leadltellurium composition containing from 59.0% to 61.8% by weight lead, and the balance substantially all tellurum, and at least one member selected from the group consisting cf, sodium, potassiurn, and thallium, in an efiective amount not in excess by weight percent of the lead and tellurim of said members as follows: 0.14 sodum; 0.23 potassium; and 0.60 thallium.

3. A compostion consisting essentially of lead and tellurium containing 59.0% to 61.8% lead by weight, balance substantially all tellurium, and contain-ng a promoter selected from the group consisting of sodium, potassium, and thal]um and contanng not more than 0.001% by weight of other matter.

4. A positive electrical conductor consisting essentially of lead and tellurium containing 59.0% to 61.8% lead by weight, balance substantially all tellurium, and contaning nat more than 0.001% by weight of other matter, except for, sodium, potassium,.and thallium in an. effective amount by weight percent thereof of the lead-tellurium not more than 0.14 sodium; 0.23 potassium; and 0.60

thalliurn, respectively.

5. A leadtellurium compositon, conssting essentally f from 59.0% to 61.8% by weight lead, and the balance substantially all tellurium, and Sediu m in an effective amount not in excess of 0.14% by weight of the lead and telluriurn.

6. A lead-tellurum compostinn, conssting essentially of from 59.0% to 61.8% by weight lead, and the balance substantially all tellurum, and potassium in an eective amount not in excess of 0.23% by weight of the 1ead and tellurium.

7. A lead-tellurium compostion, consistng essentially.

of from 59.0% to 61.8% by weight lead, and the balance substantally all tellurum, and thallium in an eective amount not in excess of 0.60% by weight of the lead and tellurium.

8. The method of controlling the electrical characteristics of a lead-tellurum composit-ion consisting essentially of from 59.0% to 61.8% lead by weight, and the balance substantially all tellurium, whch comprises alloying therewith at least one member selected from the group ccmsistng of sodium, potassium, and thallium, in an effective amount not in excess by weight percent of the lead and telluriurn of said members as follows: 0.14 sedium; 0.23 potassium; and 0.60 thallium, respectively.

9. The method of controlling the electrical characteristics of a lead-tellurium compostion consistng essen tially of from 59.0% to 61.8% lead by weight, andthe balance substantially all tellurium, which comprises alloying therewith at least one member selected from the group consisting of sodium, potassium, and thallium, 1n

an eiective amount not in excess by weigh-t percent of the lead and tellurium of sad members as follows: 0.14

sodium; 0.23 potassium; and 0.60 thallium, respectively, and thenannealing the resultant compositon at a temperature of from about 540 C. to 815 C.

No references cited. 

1. AN ALLOY CONTAINING AS TWO OF ITS ESSENTIALL CONSTITUENTS LEAD AND TELLURIUM, THE PERCENT BY WEIGHT OF LEAD BEING 59.0% TO 62.8%, BALANCE SUBSTANTIALLY ALL TELLURIUM, AND THE ALLOY CONTAINING NO MORE THAN 0.001% BY WEIGHT OTHER MATTER EXCEPT FOR LIMITED EFFECTIVE AMOUNTS OF A PROMOTER FROM THE GROUP CONSISTING OF SODIUM, POTASSIUM AND THALLIUM AFFORDING THE ALLOY REPRODUCIBLE VARIATION OF AND CONTROL OVER THE ELECTRICAL PROPERTIES THEREOF. 